Ischemia refers to a localized anemia, such as an acute condition arising from blockage in arteries supplying the affected tissue. Infarction refers to necrosis of tissue resulting from a failure in the blood supply. Myocardial infarction (MI) refers to infarction or necrosis of heart muscle tissue, frequently resulting from extended severe myocardial ischemia, such as due to occlusion of one or more coronary arteries. MI is a serious condition as the dead heart muscle results in permanent impairment and can even result in death.
If ischemia is detected before MI occurs, a variety of effective therapies and treatments are known. However, there exist several difficulties with early identification of ischemia and provision of appropriate therapies. One difficulty is that ischemic events are frequently of a silent nature, e.g., an ischemic event occurs without causing symptoms which are noticed by the afflicted person or without presenting obvious external indications. Further, ischemia can manifest as a chronic and progressive condition, such that a patient may undergo a number of ischemic episodes before becoming aware of the condition.
Once ischemia is detected, however, a number of therapies are available for effectively treating the condition and hopefully preventing progression to MI. For example, thrombolytic agents, such as tissue-type plasminogen activator (TPA), can be administered to dissolve and break-up blood clots which are a frequent cause of ischemia/MI. Angioplasty can also be performed to open blocked or occluded vessels. In the case of administration of thrombolytic agents, it has been generally shown that administration of these agents is beneficial if provided relatively rapidly (typically within three hours or less) of symptoms becoming apparent. Thus, for administration of thrombolytic agents to be most effective, the person experiencing the symptoms must usually be transported to a medical facility within a relatively brief period of time. Many thrombolytic agents are preferably delivered in a localized manner, further indicating administration by a physician. A further complication is that certain thrombolytic agents, including TPA, require controlled refrigeration to maintain their effectiveness, again indicating controlled storage and administration of such agents by clinical personnel.
A number of diagnosis techniques are known which can reveal ischemia indications, even if the ischemia has been of the silent type. For example, a surface electrocardiogram (ECG) utilizes a plurality of surface electrodes arranged in a well understood manner to monitor and evaluate a plurality of electrical vectors across the patient's body to reveal underlying physiologic activity. Ischemia typically exhibits characteristic changes in the electrophysiologic characteristics of the patient to provide indicators of the presence of ischemia. For example, characteristic changes typically occur in the ST segment, the T-wave, and/or the Q-wave. While surface ECGs are widely known and understood, they are typically limited to bedside or clinical use. Holter monitors or recorders can provide similar functionality in a portable unit to provide round the clock information without requiring continuous presence of the patient in a clinical setting. However, as external devices, Holter monitors are inconvenient to the patient and are not considered acceptable for long term continuous monitoring.
Thus it will be appreciated that there exists a need for a new system and method for early detection of ischemia, preferably before proceeding to MI. There is also a need for systems and methods not only for early detection of an ischemia condition, but also to facilitate prompt therapeutic intervention. There is a particular need for a system and method which is suitable for long term extended use by the patient, for example, in cases where ischemia may be chronic but intermittent, to provide long term monitoring without unduly inconveniencing the patient, such as via presence of an obtrusive external device. There is also a need for systems and methods to facilitate administration of time sensitive therapeutic agents, such as TPA, within the effective time window and free from the requirement that the patient be present in a clinical setting.